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9 • <br /> I <br /> Ms. Karen McLaughlin 03 March 2016 <br /> I Page 3 of 4 <br /> I City of Manteca <br /> Former Police Firing Range <br /> point collected in the area mapped as California hazardous waste (as opposed to 23 total lead data <br /> points in the RCRA waste area). By separate communication from GCI, the EHD was informed that <br /> the correlation equation between XRF data and analytical total lead data at lower concentrations <br /> caused XRF concentrations to overestimate actual total lead concentrations. GCI utilized an XRF <br /> reading of 50 mg/kg as a defining criterion (in addition to limited total lead data) between <br /> nonhazardous soil and California hazardous soil. The selected XRF concentration may be <br /> reasonable, but lacks a technical justification or demonstrated correlation to an STLC of 5 mg/I and <br /> appears to be arbitrary (why not 30 mg/kg?), resulting in the EHD's uncertainty regarding the extent <br /> of the mapped area of soil impacted by 50 mg/kg to 135 mg/kg lead and the resulting estimated <br /> volume of California hazardous waste <br /> Other chemicals of potential concern associated with other small arms firing ranges were detected <br /> in surface soil samples analyzed for the CAM 17 metals at concentrations that may exceed natural <br /> background concentrations: antimony, arsenic, copper and zinc. Samples were not collected and <br /> analyzed to establish background concentrations of these metals on the site, but general studies of <br /> background metals concentrations, notably the Kearney Foundation's Background Concentrations <br /> of Trace and Major Elements in California Soils (1996) show the possibility that the concentrations <br /> of these metals may locally exceed the average state-wide background concentrations established <br /> by that study and may warrant further elevation. <br /> Elevated concentrations of antimony, arsenic and copper were detected in selected surface soil <br /> samples at levels that exceeded ten times the STLC but were not detected in groundwater. The <br /> samples containing the elevated antimony, arsenic and copper concentrations were not analyzed by <br /> WET or TCLP, presumably because the samples contained lead exceeding the TTLC. The sample <br /> results for antimony and arsenic exceed the California Human Health Screening Level (CHHSLs) for <br /> residential use soil and the residential Regional Screening Level (RSL) established by Region IX of <br /> the United States Environmental Protection Agency (EPA); if unrestricted use of the soil is the <br /> remediation goal, these metals must be included in the confirmation sampling with the analytical <br /> method reporting limits sufficiently low to demonstrate that the remaining soil meets the criterion. <br /> The EHD requested Ms. Leona Winner of the California Department of Toxic Substances Control <br /> (DTSC) to provide additional comments on the SIR and EHD's evaluation of it. Ms. Winner noted <br /> that in a few instances, the analytical method detection limits were not below the reporting limits; <br /> this should be corrected in all future work. <br /> According to Ms. Winner, rather than the California Human Health Screening Levels (CHHSLs), the <br /> DTSC utilizes the Environmental Protection Agency's (EPA) Regional Screening Levels (RSLs) as <br /> the latter are updated more often, to characterize potential impacted soil for unrestrictive land use; <br /> she accepted the 80 mg/kg for lead as it will meet the RSL, but the other contaminants of potential <br /> concern in firing range soil, such as arsenic, antimony, copper and tin were not evaluated in SIR. <br /> The few samples analyzed for these analytes had method detection limits well above the <br /> appropriate RSLs; this should be addressed in future work to demonstrate that unrestrictive use is <br /> the appropriate designation for all residual soil following your corrective actions. <br /> To address the residual contamination issue noted above, Ms. Winners recommended collecting <br /> discreet soil confirmation samples from the floor and sidewalls of soil removal areas for analysis for <br /> all constituents of potential concern. Ms. Winner also recommended that a legal description of the <br /> area addressed by this investigation and corrective action be provided to precisely define the area <br />